1. Field of the Invention
The present invention relates to a machining jig which rotatably supports a workpiece with respect to a tool of a machine tool, and to a machining system.
2. Description of the Related Art
In general, a machine tool with a rotating table where a workpiece to be machined is placed is called a “rotary table type machine tool”. In order to precisely machine a workpiece using a rotary table type machine tool, it is necessary to reliably fasten the workpiece to the table. In relation to this, JP-A-2011-513077 proposes a machine tool with a rotary type support table which has a projection fitted into a center hole of a workpiece from below, and a friction joining type clamping mechanism which applies a pushing force to a top surface of a workpiece placed on the support table so as to strongly hold the workpiece. More specifically, the clamping mechanism of JP-A-2011-513077 is provided with an arm shaped opposing holder which can move toward a workpiece seated on the support table, a projection installed at a front end of the opposing holder so as to be fitted into a center hole of a workpiece from above, and a support part for rotatably connecting this projection to the opposing holder. When the opposing holder is moved toward the workpiece, the support part pushes the top surface of the workpiece toward the support table and rotatably holds the workpiece.
However, the projection of the support table in the machine tool of JP-A-2011-513077 is sized so as to be tightly fitted into the center hole of a workpiece, and therefore it is difficult to eject a machined workpiece by a robot or loader or other automatic device. Further, according to the machine tool of JP-A-2011-513077, positioning error of the cylinder or other drive device for driving the opposing holder causes the workpiece to be held in a state where the center hole of the workpiece is not concentric with the projection of the opposing holder. Due to this, the inlet part of the center hole of the workpiece is liable to be damaged by the projection of the opposing holder. Incidentally, when removing the projection of the support table to prevent damage to the workpiece, positioning error of the drive device of the opposing holder may cause an offset of the rotation axis of the support part from the rotation axis of the support table. In this case, slip between the top surface of the workpiece and the support part may occur during rotation of the support table, and therefore the top surface of the workpiece is liable to be damaged by the support part in the same way.
A machining jig of a machine tool which can reduce the slip between a rotating workpiece and a rotary type clamp member which pushes against the workpiece, is being sought.